摘要
金属有机高分子材料是一种应用广泛且易于加工的材料,其独特的性能使之成为先进有机高分子材料的补充。本文系统总结了这类材料在发光、光伏、导电、信息存储、液晶材料、功能陶瓷材料、纳米光刻与纳米科学以及刺激响应材料等领域的研究进展,最后对该类材料未来可能发展的方向和应用做了分析和展望。
20世纪上半叶有机高分子的合成发展使现代社会可用材料发生了革命性变化。虽然最初进展主要集中于商品化的热塑性和弹性材料领域,但到了20世纪末,重心已经逐渐转移到具有先进性能的特种材料上。随着越来越精细的高分子合成方法的出现,以及超分子化学、物理学和生物学交叉领域的快速发展,碳基高分子材料领域取得巨大进步。然而,值得注意的是,许多材料具有的性质和功能、二维或三维拓展结构,以及生物功能,都是由于金属的存在。例如用于数据存储的磁性材料、超导体、电致变色/发光材料以及包括金属元素在内的生物催化剂。因此,随着有机高分子合成的迅速发展,将金属元素嵌入到高分子链中来开发新的、易于加工的材料的想法成为可能,这也引起了科学家们的极大兴趣。虽然第一种含金属的高分子-聚乙烯基二茂铁早在1955就有报
金属有机高分子材料之所以能够迅速发展并成为先进材料领域中令人感兴趣的课题,有如下两个关键因素。首先,自20世纪90年代中期以来,新的合成方法克服了制备高分子量、可溶材料的许多障碍。这使得高分子材料和金属元素的共存成为可能。尤其是,从利用传统共价键结合金属的合成方法到使用配位键或其他非共价键方法的扩展,得到了金属高分子材料,其性质和应用也得以拓展。合成方面的进展还包括发展了金属有机高分子的可控或“活”聚合路
有机金属高分子材料一般含有主族金属,过渡金属,或镧系、锕系元素。此外,根据金属元素的位置和它们之间相互作用的性质,存在一系列不同的可能结构类型。根据金属元素的位置,有机金属高分子材料可以细分为;主链结构[

图1 金属有机高分子材料的结构多样性
Fig.1 Structural diversity of organometallic polymers
金属有机高分子是一种柔性功能材

图2 配位驱动的自组装制备球形胶束以及其绿色磷光增强机理
Fig.2 Coordination driven self-assembled spherical micelles and the green phosphorescence enhancement mechanism
前一种金属聚合物表现出强烈的绿色磷光,这与Au(I)•••Au(I)相互作用有关。随着聚苯乙烯嵌段质量分数的增加,金属聚合物的磷光强度和量子产率都出现了意想不到的提高。这是典型的聚集诱导发光现
金属有机高分子也可以在电致发光领域得到很好的应

图3 近红外电致发光材料
Fig.3 Near infrared electroluminescent materials
由于认识到地球的石油储量有限,目前人们对开发太阳能等可再生能源产生了浓厚兴趣。寻找新的高效率、低成本聚合材料应用于光伏器件是一个具有重要意义且极具挑战的工

图4 Pt(Ⅱ)聚炔与太阳能电池
Fig.4 Polyplatinynes and solar cells
考虑到金属状态的高电导率(σ>1

图5 聚铂炔与传感器
Fig.5 Polyplatinynes and sensors
在电路小型化中可以取代宏观导线导电材料的研制对于纳米电子学的发展是必不可少的。其中一个候选者便是DNA,因为它已经具有出色的自组装和分子识别能力,因此在纳米尺度上具有很大的模型化潜力。更重要的是,人们已经证明,用Z

图6 材料合成与记忆性能测试
Fig.6 Material synthesis and memory performance test
金属有机聚合物液晶材料由于其具应用前景的综合性能,而引起了人们广泛关注。研究较多的是含金属刚性棒状聚炔,它们在溶液中呈液晶

图7 几种液晶金属有机高分子材料
Fig.7 Several liquid crystal organometallic polymer materials
金属复合陶瓷是一种具有多种用途的非金属耐火材料。然而,将这些材料加工成所需形状和图案需要高温,这是一个严峻的挑战。因此,使用金属聚合物前驱体,使其易于加工成所需形式,然后热解生成特定形状/图案的陶瓷产品,是解决这一问题的一种有效方法。在20世纪90年代初,CORRIU等人证明,聚硅二乙炔与一系列过渡金属氧化物的复合材料允许在相对低温进入相应的β-SiC/金属碳化物陶

图8 功能陶瓷材料前驱体
Fig.8 Precursor of functional ceramic material
经研究发现,含有金属的均聚物对紫外线和电子束很敏感,但是对等离子体具有抵抗力,可以在表面图案化方面得到应用。例如,甲基丙烯酸酯修饰的聚二茂铁硅烷便可用紫外光进行表面图案化处

图9 纳米金阵列扫描电镜图
Fig.9 Scanning electron microscope images of nanoparticle arrays of Au
含金属嵌段共聚物在纳米光刻领域引起了广泛的关注。SCHUBERT和同事使用金属超分子二嵌段共聚物来制备生成纳米多孔薄

图10 金属超分子二嵌段共聚物制备纳米多孔薄膜
Fig.10 Preparation of nanoporous films by metal supramolecular diblock copolymers
对外界刺激响应的高分子材料也是科研工作者十分感兴趣

图11 显微镜尖端与基片连接模型及分子拉伸性能图
Fig.11 The model diagram of connecting the tip of AFM with the substrate, and the force and extension diagram of macromolecule.
金属离子的引入也使得某些有机高分子材料表现出热敏特性,这是因为它们在加热时经历了可逆的凝胶-溶胶转变[

图12 金属有机高分子材料刺激响应性能
Fig.12 Stimuli-responsive properties of organometallic polymers
由于金属有机高分子材料解决了系间穿越的禁阻问题,能同时利用单重态和三重态发光,实现了电致发光100%的内量子效率,这极大地优化了能量利用,同时也为某些前沿领域(例如,电泵浦激光)的进一步研究提供了可能。能源问题一直都在世界范围内受到较大关注,而太阳能电池的发展不仅有助于人类在未来面对能源危机,而且还将缓解由于大量化石能源燃烧造成的环境污染问题。随着科研工作者的不断研究,金属有机高分子材料应用于太阳能电池所获得的光电转换效率不断提升,在光伏材料领域占据着重要地位。在后续的研究中,研究者们将致力于设计、合成与太阳光谱范围有更高重合度、载流子的迁移率更高的新的聚合材料,以实现制造高效率、低成本的光伏器件。刺激响应材料也被称作“智能”材料,由于这类材料可以感受外部环境的变化,如温度、光照、压力、pH值,或一些特定物质,从而导致这些大分子的物理化学特性和功能状态发生较大转变,同时向外部反馈一些可检测或可视的信号,利用这种功能行为的变化可以制备出不同的功能材料,使得它们成为研究热门。大量的研究结果表明,刺激响应聚合物在纳米材料科学、生命科学及临床医学领域中有着广泛的应用前景,同时也对材料的灵敏度、特异性等方面提出了更高的要求。
尽管如此,在这一迅速扩大的领域,充满机遇的同时也面临着许多挑战。例如,更多新型有机高分子的设计对合成手段也提出了更高的要求;同时,在材料使用过程中如何保证材料的稳定性和使用寿命也是研究的热点问题。
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